Certain applications require measuring aspects that are based on the speed of light.
For example, range finding can be carried out using optics. An optical signal is sent. The reflection therefrom is received. The time that it takes to receive the reflection of the optical signal gives an indication of the distance.
The so called lock-in technique uses an encoded temporal pattern as a signal reference. The device locks into the received signal to find the time of receipt. However, noise can mask the temporal pattern.
A lock in photodetector based on charged coupled devices or CCDs has been described in Miagawa and Kanada xe2x80x9cCCD based range finding sensorxe2x80x9d IEEE Transactions on Electronic Devices, volume 44 pages 1648-1652 1997.
CCDs are well known to have relatively large power consumption.
The present application describes a special kind of lock in detector formed using CMOS technology. More specifically, a lock in detector is formed from a pinned photodiode. The photodiode is modified to enable faster operation.
It is advantageous to obtain as much readout as possible to maximize the signal to noise ratio. The pinned photodiode provides virtually complete charge transfer readout.
Fast separation of the photo-generated carriers is obtained by separating the diode into smaller sub-parts and summing the output values of the subparts to obtain an increased composite signal.